This invention relates to a composite fiber formed of a sheath and core, adapted particularly for knitting, weaving or floccing wherein the core is a fiber or monofilament and the sheath enveloping the core is a cellular and pervious foam contiguous with, and adjacent, the core, and a microcellular less pervious foam at, and adjacent to, the outer perimeter of said sheath, the surface of which is regular and continuous in appearance. The invention relates, as well, to a method for producing these composite or conjugate fibers.
Combinations of foam and fiber have been known heretofore. The production more particularly of flexible cellular foam fibers having an outer envelope of woolen yarn or a combination of wool and synthetic fibers has been described heretofore, illustratively, in U.S. Pat. No. 3,287,892. The resulting product does not however present an outer surface of skin resistant to abrasion and inherently resistant to attack by moths or the like. The product also attains normally a reduced bulk without an economic use of materials; an incident of the use of the woolen fiber to define the outer surface rather than the core.
It has also been known to provide a cellular structure in which are disposed a plurality of glass fibrils, that involves coating glass fibrils with a thermoplastic polyurethane solution, immersing the coated product in a higher-boiling, miscible, non-solvent for the thermoplastic resin and heating this composition to drive off the initial solvent in which the resin is dissolved; forming the precipitated thermoplastic polyurethane and disrupting the invested glass fibrils. The product, as will be evident, cannot be woven, spun or knit; and presents a weakened product in solvent-susceptible state that cannot be dry cleaned by any conventional treatment means and has an abrasion-resistance that would render it vulnerable to excessive wear even when subject to washing.
Modifying a fiber to yield a porous irregular surface thereon is known and described in U.S. Pat. Nos. 2,862,284; 3,278,329; 3,889,038; and 4,010,308. The use of these fibers in standard spinning and weaving procedures is, however, severely inhibited or prevented by the induced irregularity of the fibers' surface; and their use in apparel, for example, limited by their lack of abrasion resistance.
The production of a foam mass incorporating a reticulum of polyamide, polyester or polyolefin fibers and forming a sheet or mat is also well known heretofore. Mats or sheets, such as the foregoing are described in U.S. Pat. Nos. 3,474,049; 3,474,050; 3,474,051; and 3,480,569 and utilize ratios of foaming components to fiber such that the volume of foam effectively exceeds that generally conceded to be desirable in formulating a discrete foam-covered fiber.
The length to diameter ratio of the individual fibers forming the network of the patentees' mats is also recited as not exceeding 10,000 to assure a continued adhesion between the fibers and surrounding foam. This length is however inadequate for the purpose of providing fibers for spinning, weaving or the like. The surface of the mats produced by the patentees will also be porous and irregular.
Accordingly, if a composite fiber or filament could be produced, and a process evolved for its preparation, having a continuous core fiber and adhering thereto an inner cellular thermoset sheath composed of a low density ply terminating at its outer perimeter in a high density ply having a smooth regular and continuous outer "skin" of limited porosity with accompanying superior abrasion- and tear-resistance properties, the result would be a significant advance in the state of the art.
If, additionally, the composite fiber and filaments so formed were capable of modifying or masking the undesired properties of the core fiber while providing significant integration of the inner and outer sheath with one another and with said core fiber, for example, and providing in contrast with the core fiber alone, improved bulking, pleasant and warm hand, ready dyeability, decreased crushability, increased resiliency, less hygroscopicity and better wet properties and yet fibers that are readily woven, spun or flocced the advance manifested in the art would be significant indeed.